Patent GB-405281-A (GB)
Title: Improvements in telegraph or telephone systems using in part sound or elastic waves as the agency of communication
IPC: G10K11/24
Filed: 1932-07-26
Abstract: 405,281. Signalling by audible signals. PIERCE, G. W., Harvard University, Cambridge, Massachusetts, U.S.A. July 26, 1932, No. 6156/33. Divided on 405,613. [Class 118 (ii).] Sound or like audible or inaudible vibrations are transmitted by longitudinal vibrations along a solid conductor such as a wire, the vibration energy at the receiving end being converted into electric energy. The vibrations may be imparted to the transmitting end of the vibration conductor directly or by a diaphragm or through the medium of magneto-strictive vibrators, electrostatic vibrators, or an electromagnet and diaphragm. At the receiving end, the mechanical vibrations are converted into electric vibrations and ultimately into audible sound waves by magneto-strictive vibrators or a resistance changing device such as a carbon-granule microphone, or a piezo-electric crystal or an electromagnet and diaphragm. The apparatus may be applied in connection with directional transmitting and receiving apparatus as described in Specification 405,613. Mechanical vibrations may also be independently transmitted through electric conductors. In the system shown in Fig. 1, the ends of the mechanical vibration conductor 4 are connected to transmitting and receiving magnetostrictive cores 2, 5. At the transmitting end, several series-connected inductive coils 10, spaced in accordance with the transmitting periodicity, receive high frequency electric oscillations from a vacuum tube oscillator 30 and produce mechanical vibrations of the same periodicity in the wire 4. The electric oscillations may be modulated by speech in the microphone 70 by means of transformers 66, 68 and an amplifier 67 or by other means. At the receiving end, the mechanical vibrations of the magneto-strictive core 5, produces electric oscillation in the series connected induction coils 6 which are coupled suitably as by the transformer 76, 77 to thermionic valve amplifiers 74, 32, 34 and a detector valve 36 connected to a telephone receiver 44 or loud speaker 69. The various alternatives to magneto-strictive transmitting and receiving means referred to previously are shown in the drawings. Mechanical vibration may be transmitted independently through the electro-conductor 100, Fig. 12, by rods 102 of glass or other insulating material connected to magnetostrictive cores 2, 5 associated respectively with transmitting and receiving apparatus. A single wire 4 may carry a number of independent vibrations of different periodicity each associated with a separate tuned receiver. When used in conjunction with directional receiving or transmitting diaphragms as described in Specification 405,613, a number of points situated at or near the outer nodes on the diaphragm are connected by wires to a common convertor of sound into electric energy. If the wires are all of equal length, the several connections must be made at points in the same phase, but if they are of unequal length, as shown in Fig. 10, the connection must be made at slightly different phase points to obtain the maximum effect at the proper incident angle. The diaphragm may be constructed to transmit sound only in directions normal to its surface by constructing it of very thin metal or of rubber so that it has very little transverse rigidity. Each wire may then terminate in a small metallic diaphragm 88. The direction of a sound source may be determined, without adjusting the diaphragm angularly, by altering the length of the sound paths from the diaphragm to the magneto-strictive or other transformation apparatus, as shown in Fig. 11. The windings 94 are mounted on an angularly adjustable arm 96 having a pointer 98. The free ends of the magneto-strictive wires 92 are made long so that any reflected waves are attenuated before returning, thus avoiding the possibility of the formation of nodes or loops in the neighbourhood of the take off coils 94. Specification 313,031, [Class 37, Electricity, Measuring &c.], is referred to.